Studies have been focused on population-based cohorts in the United States and Europe. A six-year study of hearing levels in the U.S. began in April 1999, the Fourth National Health and Nutrition Examination Survey (NHANES IV), 1999-2004. The ESDS Branch has collaborated with staff of the National Institute for Occupational Safety and Health (NIOSH) in developing the protocol and data collection instruments for this study of adults, 20 to 69 years of age. Information is collected by two different examination teams in MECs (mobile exam centers that are specially equipped trailers) deployed in randomly selected communities across the U.S. Air conduction, pure-tone hearing thresholds are obtained from subjects in sound-treated booths, and responses to questionnaires on difficulties with hearing (and tinnitus), are obtained by the National Center for Health Statistics (NCHS) as part of a larger multifaceted examination and interview survey. This year we have been able to review results from the first year of testing. No public use dataset will be available for analysis and publication of findings until after the first three years of data collection have been completed, in order to insure an adequate sample size for national estimates of hearing impairment. These data are especially important since no hearing tests for a national sample of the U.S. adult population have been conducted since NHANES I, 1971-1975. Analyses have continued this year on a large cohort of adults in a hearing examination study conducted in Nord Trondelag, Norway as part of a larger health examination study (HUNT II). NIDCD and the Norwegian Public Health Institute (Folkehelsa) have jointly supported this study. An analysis comparing otoacoustic emissions test results with pure-tone thresholds was completed on a sample of subjects and a paper has been submitted for publication. Also a paper has been submitted for review to an epidemiological journal that describes the effects of age, sex, noise exposure, recurrent ear infections, and head injuries on pure-tone average hearing levels in low (250 and 500 Hz), middle (1000 and 2000 Hz) and high (3000, 4000, 6000, and 8000 Hz) frequencies. Both linear multiple regression and multivariable logistic regression were used in the analysis. Hearing impairment increased with age and was higher for men versus women. Almost no effect of noise exposure could be detected in women less than 45 years old. There were persistent effects attributable to recurrent ear infections and head injuries. In men 45 years old or greater, the ten percent with the largest occupational noise exposures had, on average, 8 dB worse hearing levels in both the middle and high frequency ranges. In another analysis, the high frequency thresholds (4000 and 6000 Hz) obtained from this unscreened population-based sample were compared to international standards in use as norms for screening individuals for noise-related hearing loss. We concluded that this unscreened male population, with minor adjustment, provides threshold values that are similar to the screened international standard for younger subjects, less than age 55, but could not be easily adapted at older ages. We have also collaborated with a Danish researcher who has conducted population-based health interview studies on adult twin subjects. Using structural equation analyses suitable for twin samples, we have estimated the hereditability of reported hearing loss to be 45-52%. A paper describing the findings for the oldest subjects, 75 years of age or older, has been completed. Additional information about adult hearing levels in the U.S. will be collected through the Year 2001 National Health Interview Survey Supplement on Hearing. The ESDS Branch collaborated with NCHS in developing the questionnaire for this survey. The information obtained will be used as a baseline for Healthy People 2010, in order to set goals and monitor progress for preventable hearing impairment in the U.S. adult population.